This invention relates to a method and apparatus for pretreating a lumen with a source of peroxide before sterilization at low pressure in a chamber.
Medical instruments have traditionally been sterilized using either heat, such as is provided by steam, or a chemical, such as formaldehyde or ethylene oxide in the gas or vapor state. Each of these methods has drawbacks. Many medical devices, such as fiberoptic devices, endoscopes, power tools, etc. are sensitive to heat, moisture, or both. Formaldehyde and ethylene oxide are both toxic gases that pose a potential hazard to healthcare workers. Problems with ethylene oxide are particularly severe, because its use requires long aeration times to remove the gas from articles that have been sterilized. This makes the sterilization cycle time undesirably long.
Sterilization using liquid hydrogen peroxide solution has been found to require a high concentration of sterilant, extended exposure times and/or elevated temperatures. However, sterilization using hydrogen peroxide vapor has been shown to have some advantages over other chemical sterilization processes (see, e.g., U.S. Pat. Nos. 4,169,123 and 4,169,124). The combination of hydrogen peroxide with a plasma provides certain additional advantages, as disclosed in U.S. Pat. No. 4,643,876, issued Feb. 17, 1987 to Jacobs et al. U.S. Pat. No. 4,756,882, issued Jul. 12, 1988, also to Jacobs et al. discloses the use of hydrogen peroxide vapor, generated from an aqueous solution of hydrogen peroxide, as a precursor of the reactive species generated by a plasma generator. The combination of hydrogen peroxide vapor diffusing into close proximity with the article to be sterilized and plasma acts to sterilize the articles, even within closed packages. Further, these methods of combining hydrogen peroxide vapor with a plasma, while useful in xe2x80x9copenxe2x80x9d systems, have been found to be inadequate to effect sterilization in articles having diffusion-restricted areas, since the methods are dependent upon diffusion of the sterilant vapor into close proximity with the article before sterilization can be achieved. Thus, these methods have been found to require high concentration of sterilant, extended exposure time and/or elevated temperatures when used on long, narrow lumens. For example, lumens longer than 27 cm and/or having an internal diameter of less than 0.3 cm have been particularly difficult to sterilize. Thus, no simple, safe, effective method of sterilizing smaller lumens exists in the prior art.
The sterilization of articles containing diffusion-restricted areas, such as long narrow lumens, therefore presents a special challenge. Methods that use hydrogen peroxide vapor that has been generated from an aqueous solution of hydrogen peroxide have certain disadvantages, because:
1. Water has a higher vapor pressure than hydrogen peroxide and will vaporize faster than hydrogen peroxide from an aqueous solution.
2. Water has a lower molecular weight than hydrogen peroxide and will diffuse faster than hydrogen peroxide in the vapor state.
Because of this, when an aqueous solution of hydrogen peroxide is vaporized in the area surrounding the items to be sterilized, the water reaches the items first and in higher concentration. The water vapor therefore becomes a barrier to the penetration of hydrogen peroxide vapor into diffusion restricted areas, such as small crevices and long narrow lumens. One cannot solve the problem by removing water from the aqueous solution and using more concentrated hydrogen peroxide, since, among other reasons, concentrated solutions of hydrogen peroxide greater than 65% by weight can be hazardous due to the oxidizing nature thereof.
U.S. Pat. No. 4,952,370 to Cummings et al. discloses a sterilization process wherein aqueous hydrogen.peroxide vapor is first condensed on the article to be sterilized, and then a source of vacuum is applied to the sterilization chamber to evaporate the water and hydrogen peroxide from the article. This method is suitable to sterilize surfaces, however, it is ineffective at rapidly sterilizing diffusion-restricted areas, such as those found in lumened devices, since it too depends on the diffusion of the hydrogen peroxide vapor into the lumen to effect sterilization.
U.S. Pat. No. 4,943,414, entitled xe2x80x9cMethod for Vapor Sterilization of Articles Having Lumens,xe2x80x9d and issued to Jacobs et al., discloses a process in which a vessel containing a small amount of a vaporizable liquid sterilant solution is attached to a lumen, and the sterilant vaporizes and flows directly into the lumen of the article as the pressure is reduced during the sterilization cycle. This system has the advantage that the water and hydrogen peroxide vapor are pulled through the lumen by the pressure differential that exists, increasing the sterilization rate for lumens, but it has the disadvantage that the vessel needs to be attached to each lumen to be sterilized. Potentially, the area between the vessel and the lumen may be occluded from the sterilization process. In addition, water is vaporized faster and precedes the hydrogen peroxide vapor into the lumen.
In U.S. Patent. No. 5,492,672, there is disclosed a process for sterilizing narrow lumens. This process uses a multicomponent sterilant vapor and requires successive alternating periods of flow of sterilant vapor and discontinuance of such flow. A complex apparatus is used to accomplish the method. Because flow through of vapor is used, closed end lumens are not readily sterilized in the process.
Thus, there remains a need for a simple and effective method of vapor sterilization of articles having areas where diffusion of these vapors is restricted, such as long, narrow lumens.
One aspect of the present invention relates to an apparatus for pretreating a lumen. The apparatus comprises a connector containing hydrogen peroxide, where the connector is attached to one end of the lumen, means for creating a pressure difference between the connector and the second end of the lumen, where the second end of the lumen is at a lower pressure than the connector, causing the hydrogen peroxide to flow through the lumen.
In one embodiment, the hydrogen peroxide is a liquid. Preferably, the apparatus also includes a receptacle containing a liquid comprising hydrogen peroxide, where the receptacle is attached to the connector. In another aspect, the connector is collapsible.
In another embodiment, the hydrogen peroxide is a mist or aerosol. Advantageously, the apparatus additionally comprises a generator of mist or aerosol, where the generator of mist or aerosol is attached to the connector in a manner allowing the mist or aerosol to enter the connector.
In one embodiment, the generator of mist or aerosol is a humidifier. Preferably, the humidifier comprises an ultrasonic transducer. In other embodiments, the generator of mist or aerosol comprises a liquid spray nozzle, a tank containing a liquid comprising hydrogen peroxide with a gas nozzle situated at least partially in the liquid, or a nebulizer.
Preferably, the means for creating the pressure difference between the connector and the second end of the lumen is a source of vacuum.
Advantageously, the apparatus for pretreating the lumen additionally comprises a vacuum chamber capable of vaporizing hydrogen peroxide and a source of sterilant located in an enclosure, where the enclosure is in fluid communication with the chamber and is able to introduce sterilant into the interior of the chamber. Preferably, the sterilant comprises hydrogen peroxide.
Advantageously, the apparatus additionally comprises a source of plasma. Preferably, the apparatus additionally comprises a heat source to heat the enclosure.
Another aspect of the invention is a method of pretreating and sterilizing the interior and exterior of a lumen comprising contacting the interior of the lumen with a liquid comprising hydrogen peroxide, where the liquid is delivered from a source of liquid, placing the lumen in a chamber, where the placing occurs before or after contacting, removing the source of liquid from the lumen, evacuating the chamber, where the source of liquid is removed before evacuating, introducing sterilant into the chamber from an enclosure in fluid communication with the chamber, vaporizing the liquid in the interior of the lumen, and sterilizing the interior and exterior of the lumen.
In a preferred embodiment, the contacting can occur via one or more of the following methods: direct delivery, injection, static soak, liquid flow-through, aerosol or mist, condensation, or physical placement.
Advantageously, the lumen is also exposed to a plasma. The plasma may be generated in the chamber with the lumen, or it may be generated in a second chamber and flowed into the chamber with the lumen. Preferably, the sterilant comprises hydrogen peroxide.
In one aspect of the invention the contacting of the interior of the lumen with the liquid comprising hydrogen peroxide comprises attaching a collapsible container containing a liquid comprising hydrogen peroxide to an end of the lumen, and generating a pressure difference between the collapsible container and the other end of the lumen, where the other end is at a lower pressure than the container, collapsing the collapsible container and contacting the liquid with the interior of the lumen.
In another aspect of the invention, the contacting with the interior of the lumen comprises attaching a container containing a liquid comprising hydrogen peroxide to an end of the lumen and generating a pressure difference between the container and the other end of the lumen, where the other end of the lumen is at a lower pressure than the container.
Alternatively, the contacting can occur by generating a mist or aerosol comprising hydrogen peroxide, flowing the mist or aerosol into a connector attached to a first end of the lumen, and generating a pressure difference between the connector and the other end of the lumen, where the other end of the lumen is at a lower pressure than the connector, thereby contacting the interior of the lumen with the mist or aerosol.
In another aspect of the invention, the sterilant is introduced into the chamber before or during the vaporization of the liquid in the lumen. Advantageously, the introducing the sterilant from the enclosure is a concentrating process. Preferably the sterilant is generated from a source of sterilant. Advantageously, the source of sterilant is a liquid peroxide or a solid peroxide complex. The source of sterilant may be introduced into the enclosure either before or during evacuation.